Field of the Invention
The present invention relates to an injection mold in whose cavity molten resin meets.
Description of the Related Art
In resin car parts, the painting has been applied on many decorative parts corresponding to design parts. However, due to problems of a cost increase and the generation of VOC (Volatile Organic Compounds) caused by the painting step, the adoption of unpainted parts molded from colored materials that are resin materials directly colored with coloring agents such as pigments or dyes has been increasing year by year. Especially as car interior parts, resin parts with metallic color are often adopted, which has given rise to a demand for realizing a cost reduction of resin parts with a metallic tone by eliminating the painting.
In resin injection molding, leading ends of flows of molten resin are likely to become cold, and when they meet each other in a solidified state, defective welding occurs, leading to an appearance defect and strength reduction. A linear pattern generated by such meeting of the molten resin is called a weld line. When a hole shape or the like exists in a multi-point gate or a part, diffluence and confluence of the molten resin occur, leading to the generation of the weld line. Ordinary methods for correcting the weld line include a method of setting mold temperature or resin temperature high or setting injection speed high, thereby preventing leading ends of flows of molten resin from solidifying, but even by such a method, it is difficult to completely eliminate the weld line. Especially an unpainted resin part with a metallic tone using colored resin containing a luminous material has a problem that the orientation of the luminous material is disordered by the collision of the molten resin and as a result it loses a luminous feeling to appear black, so that the weld line becomes dark to be emphasized, leading to a serious appearance defect.
As a technique to solve this kind of problem, Patent Document 1, for instance, discloses a structure in which one of two resin flows running in opposite directions from a gate flows out to a resin reservoir before reaching a meeting part, in a cavity having a ring shape in a plane view. Patent Document 1 says that this structure increases a meeting angle of one and the other of the resin flows and can prevent the generation of a weld line.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2008-188855
However, the method disclosed in Patent Document 1 cannot alleviate the disorder of the orientation of a luminous material when the two resin flows meet each other.